Party line selective signaling system having code and conference call



May 15, 1951 c. E. LOMAX 2,552,799

PARTY LINE SELECTIVE SIGNALING SYSTEM HAVING CODE AND CONFERENCE CALL Filed Dec. 50, 1947 12 Sheets-Sheet l FIG. I

INVENTOR. C\orence E. LomCx LINE EQUIPMENT May 15, 1951 c. E. LOMAX PARTY LINE SELECTIVE SIGNALING SYSTEM HAVING CODE AND CONFERENCE CALL Filed Dec. 50, 1947 I 12 Sheets-Sheet 2 FIG.||

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MOT. ST-n T6 OTHER STATIONS 2 KEY CONFERENCE INVENTOR. Cmrence E.Lomnx May 15, 1951 c. E. LOMAX 2,552,799

PARTY LINE SELECTIVE SIGNALING SYSTEM HAVING CODE AND CONFERENCE CALL Filed D80. 50, 1947 12 Sheets-Sheet 5 clso SECOND GROUP TO OTHER STATIONS A l A 1 OTHER STATIONS TWO GROUP CONFERENCE INVENTOR.

Clarence E. Lomox AHy.

May 15, 1951 I c. E. LOMAX 2,552,799

' PARTY LINE SELECTIVE SIGNALING SYSTEM HAVING CODE AND CONFERENCE CALL Filed Dec. 30, 1947 12 Sheets-Sheet 4 c170 CITOq Claw 2m \C|8O C I mzol llzsl 272w. r ..Al

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PARTY LINE SELECTIVE SIGNALING SYSTEM HAVING I CODE AND CONFERENCE CALL Filed Dec. 50, 1947 12 Sheets-Shee 10 o a" o o INVENTOR. Clarence E. Lomux BY .wm m 22 5& m mmm mmm Oww Ohm @5958 88 W v8 W ofi ON mw E mmw 6E 5, m: v z M58 38% in 1 nub mt. t, r mm www 0 33 M58 w mu o May 15, 1951 c. E. LOMAX PARTY LINE SELECTIVE SIGNALING SYSTEM HAVING CODE AND CONFERENCE CALL l2 Sheets-Sheet ll Filed Dec.

F IG. ,MULTI GROUP CONFERENCE o o t -o o nounoo aoo .INVENTOR. Clarence E. Lomax lgzso gar May 15, 1951 c. E. LOMAX 2,552,799

PARTY LINE SELECTIVE SIGNALING SYSTEM HAVING CODE AND CONFERENCE CALL Y FIG. IO

M'ULTI GROUP CONFERENCE TO GROUP *1; 262

TO GROUPW'ZQ I 263 TO OTHER GROUPS INVENTOR.

Clarence .E. L omox Patented May 15, 1951 PARTY LINE SELECTIVE SIGNALING SYS- TEM HAVING CODE AND CONFERENCE CALL Clarence E. Lomax, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application December 30, 1947, Serial No."794,601

1 9' Claims.

The present invention relates in general to automatic telephone systems, but is more particularly concerned with small systems which are commonly known as private automatic exchanges, or as a P. A. X. Exchanges of this na" ture are usually installed by private concerns, and in order to meet the more exacting requirements of the subscribers in these small systems, it is often necessary to provide various special features which are unnecessary in a large public exchange. The present invention is concerned with the above-mentioned special features which are commonly known as code calling, conference calling, executive cut-in or right-oi-way and party line service. i

The principal object of the invention is to provide certain new and improved circuit arrangements, whereby, the above-named special features are provided without materiallyv increasing the cost of the equipment, while retaining simple, efficient and modern high-class telephone servme.

One of the features of the invention relates to improved circuit arrangements, whereby, the rotary switch as described in the co-pending application of Kenneth W. Graybill et al., Serial No. 654,556, filed March 15, 1946, is utilized in applicants illustrated finder, connector, code call and conference call equipment.

Another feature of the invention relates to an improved line equipment and circuit, whereby during conference calls other parties on the lines that contain a conference member are totally disconnected from their respective lines during the conference call.

Another feature of the invention relates to improved circuit arrangements, whereby, party line service, code call, conference service and executive cut-in service can all be given in the same exchange.

Still another feature relates to conference service, whereby, various types of conference service can be provided, with the requirements of the particular exchange controlling the type service to be used.

Other features, together with the ones named above, will be explained hereinafter, reference being had to the accompanying drawings which show by means of the usual circuit diagrams a sufficient amount of apparatus to enable the invention to be described and understood.

Referring now to the drawings, Figures 1 to 15, inclusive:

Figure 1 shows four lines having two substations each, such as A and A on one line and D and D on another, etc. Substations A, B and C are shown as conference members, hence, the cut-through relays such as I00, Hi3 and I2?! are provided. Substation A is shown as belonging to an executive and is provided with the executive cut-in non-locking push button H8. Substation A is also provided with the non-locking push button it which enables the originating of the key-type conference call (push button IE8 is used only when Figure 2 is a part of the exchange). The line containing substations D and D is provided with no special features and therefore, only local or regular calls can be handled.

Combined line and cut-off relays such as I30, Mil, I59 and I 6B are individual to each line.

Figures 2, 2A and 2B are used only when the exchange is to include conference calling, each of the Figures 2, 2A and 23 being individual to a certain type of conference service. It is to be remembered that only one type conference can be used at a time, therefore, only one of the Figures 2, 2A or 23 can be used at a time. It will be noted that each of the figures have been drawn so as to be easily substituted for the other and to readily connect between Figure 1 and the adjoining figures. It will also be noted that thering cut-off and battery feed relays individual to each line that is provided with conference service, are given the same number and location in each of the figures and that the functions of the above mentioned relays are identical in each figure. However, the relays in the respective right-half portions of each figure are different. In Figure 2 a single conference group is provided, substations A, B, and C being the conference members, with one of the substations such as A having a key for initiating the conference call. In Figure 2A two-conference group service is shown with substations A and C being individual to groups I and 2 respectively and substation B being common to both groups. In Figure 2B multi-group conference service is shown, with only two groups illustrated. Substations A and C are again in different groups and substation B is common to both.

Figures 3 and 4 show one of the finder-connector links of the exchange.

Figure 5 shows the distributor.

Figures 6, '7, and 8 show the code call equipment, with Figure 6 showing the code call finder, Figure 7 showing the pulsing circuit and code selecting equipment and Figure 8 showing the code sounding equipment.

Figures 9 and 10 show the multi-group conference equipment, with Figure 9 showing the group conference finder and Figure shows the group selecting equipment.

Figures 11, 12, 13, 14 and 15 are figure-number diagrams and show the drawing arrangements for the descriptions of the sections entitled Regular P. A. X service, Key conference, Code call, Two group conference and Multi-group conference, respectively. y

Having briefiy described the apparatus involved in each figure, a more detailed description of the various operations will follow:

It is to be remembered that the maximum number of lines served by an exchange of this type is lines, and the number of finder connector links may be limited to not more than four. Four lines have been shown, with two parties each and so arranged as to be rung on the opposite sides of the lines. The equipment at each sub-station consists of the well-known, dial, receiver, transmitter and, ringer, therefore only the ringer connections at each substation have been shown, likewise the illustrated substations call numbers. All regular call numbers are twodigit numbers and assuming that a full capacity of 20 lines are in use and also assume ing each line has two parties the call numbers will be arranged in the following order: the digits 31 to and 41 to will be used for the first group of ten lines and the digits 51 to and 61 to will be used for the second group of ten lines. the ringing to be applied to the positive line conduotors and the digits 41 to. 40 and 61 to 60,wi1l cause ringing to be appliedto, the negative line conductors.

A rotary switch having 26 positions with 25 bank contacts has been utilized wherever applicable in the exchange. The 26th position is the normal home position for the wipers, while the first and second contacts of the connector rotary switch may be used for either code call or two-group conference service, the third and fourth contacts of the same switch utilized for the first digit of the call number when dialing the first group of ten lines and the 15th contact is used as a stopping point for the first digit of the call number when dialing the second group of ten lines. Thus, it will be seen that the first group of ten lines uses contacts 5 through 14 and the second, or last, group of ten lines uses contacts l6 through 25. The rotary switch of the finders (including the code call finder and conference call finder and group selector) are of the non-numerical type and therefore do not use the 26th or home position, whereas, the rotary switch of the connector and code ringing selector are numerical and do use their home positions.

Referring to Figure l for the present, the combined' line and cut-off relays such as I353, M2, 3

next free or idle finder-connector link after each.

normal operation. Therefore during normal operating periods of the exchange, the wipers of the rotary switch will be resting on an idle link. A busy link will apply a ground potential to the Wipers and hence complete a circuit to the rotary The digits 31 to 30 and 51 to 50. will cause.

switch motor magnet to cause the magnet to step its wipers off the grounded contact. Therefore, it will be seen that the motor magnet causes the switch to hunt for an absence of ground on its Wipers.

It will be remembered that in the illustrated exchange, energization of all the rotary switch motor magnets only prepares the switch for stepping and that the actual stepping of the switch takes place upon the deenergization and release of the magnet.

The illustrated finder-connector link (Figures 3 and 4) has beendrawn showing alternative connections to the finder and connector for an exchange including two-group conference service, or multi-group conference service, or code call service, the type of special service used being dependent on the requirements of each individual exchange.

Referring to Figures 6, 7, and 8 the finder (Fig. 6) of the code call equipment functions. nearly the same as the line finder inFigure 3 with,v

the exception that it searches for a ground potential by way of its extra control (EC) conductor instead of the control (C) conductor. The rotary switches shown in Figure '7 operate under pulsing during dialing of the code call number. As only the first five switches are used, and the code call number contains two digits; the number of codes that can be sent is limited to 25. mum digital value that either digit can attain is 5. From the foregoing it will be understood that the lowest code call number will be 11 and the highest will be 55,. The rotary switches in Figure 8 are of the previously mentioned 25 point type. The push button such as 865 may be conveniently located throughout the building or buildings within which the exchange is installed and may be operated for sounding special alarms such as fire, dismissal signals, etc. The alarms or gongs such as 878 and 88%! (as many may be used as necessary) are also conveniently located so as to be clearly audible to everyone.

Referring to Figures '9 and 10 showing the multi-group conference equipment, the conference finder (Figure 9) functions the same as the code call finder. The 26 point rotary switch shown in Figure 10 responds to the group number dialed. As the switch is shown, it is wired for five conference groups, however, it may be wired to include ten conference groups, if desired. From the foregoing, it will be understood that the conference group call number is a single digit and may extend from 1 through 0, though the drawing shows it to be limited from 1 through 5.

The figure-number diagrams 11 through 15 show the arrangement of the drawings for regular, or local, calls and for each'special service. It will be remembered that regular calls may be made with each special service or combination of special services.

A detailed operational description of regular calls and all special services will follow, references being had with the drawings which show suifi- .cient apparatus as deemed necessary for each ex planation.

' Regular P. A. X service The operation of the equipment (excluding all special services) as to the initiation and completion of a regular P. A. X call will now be discussed.

Referring in particular to the figure-number diagram of Figure 11 and its, associated drawings comprising Figures 1, 3, 4, and 5, sumcient appacontacts of the above-named Therefore, the maxiratus of the system is shown as deemed necessary for the explanation.

Assuming that subscriber B is given a designated call number such as 32 and that subscribor D desires to call subscriber B, the equipment will operate in the following'manner:

When subscriber D removes the receiver, a loop is closed across his talking conductors and a circuit is completed to the line and cut-off relay I60, this circuit extending from ground at contacts I63, the associated positive talking conductor, the loop circuit, the associated negative talking conductor, contacts I 5|, upper Winding of relay I60 and the lower Winding of relay I50 to battery. As previously described, the relay I66 is a two-step line and cut-off relay having two serially connected windings, capable (during the present energization) of causing the relay I60 to close only the as contacts. At as contacts i62, relay I60 applies battery potential to the control conductorl56. At 01: contacts I55, relay I65 applies a ground potential to the distributor-start conductor I90, completing a circuit to the distributor-start conductor I50, completing a circuit to the distributor-start relay 5I0 (providing that the wipers of the distributor motor magnet 515 are resting on an idle finder-connector link), this circuit extending from ground at contacts I64,

: contacts I65, conductor I96, contacts 502,

high resistance winding of distributor-start relay I0, contacts I, 516 and through the marginal winding of motor magnet 515 to battery. Magnet 515 will not operate in series with relay 5I0.

As previously mentioned, the distributor is of the rotary type and after each normal operation preselects the next idle or free finder-connector link, therefore wipers 505 and 506 of the associated motor magnet 515 will rest on an idle or free link. However, if all links were busy at the moment, the operating circuit of the all-links-busy relay 500 would be open due to the absence of ground potential (supplied by any idle or free link from ground at contacts such as 354 in Figure 3) on the conductor 551 to relay 550. Relay 505 would then restore and open the circuit to motor magnet 515 at contacts 50I, thereby preventing motor magnet 515 from operating. However, as soon as a link becomes free, the ground potential is restored to the conductor 551 and relay 500 will operate and prepare a circuit to motor magnet 515. This circuit will be completed if wiper 505 is resting on a contact terminating the guard lead of a busy link, but if the wiper is resting on a contact terminating the guard lead of an idle link, the circuit will not be completed. As shown in Figure 5, the wipers 505 and 566 of magnet 515 are resting on the contacts of the illustrated finder-connector link (Figures 3 and 4) which is shown as idle.

In operating contacts 5| I, distributor start relay 5I0 opens apoint in the ener izing circuit of motor-magnet 515, at contacts 5I2 ground is removed from a secondary kick-off circuit which is under control of the calling subscriber and relay 530, at contacts 5I3 a circuit is completed for relay are which at the moment is slightly slow to operate due to its short circuited upper winding. At contacts 5I4 relay m applies a ground to the multiple circuit for maintaining relay 560 operated, at contacts 5I5 prepares an operating circuit for the relay 555 and at-contacts 5I6 completes an obvious preenergizing circuit for relay 550. Resistance R2 is high enough to prevent relay 550 from operating, but making relay 550 quick-acting to any "splash of current through its upper winding and operative for any such splash.

In operating, relay 520 completes a circuit for the slow to operate relay 530, from ground at contacts 52I and at contacts 522 prepares a circuit for relay 550.

' In operating relay 530 completes a circuit to the finder-start relay 320 (Figure 3) at contacts 53!, this circuit extending from ground at contacts 53I, wiper 506 and its associated contact, conductor 541 and the winding of relay 320 to battery. At contacts 532 relay 530 prepares a. circuit for motor-magnet 515, at contact 533 a kick-off circuit is prepared for motor-magnet 515, at contacts 534 the circuit of the upper winding of relay 520 is opened, thereby giving relay 523 a normal quick restoring time interval. At contacts 535 relay 530 connects a ground to the multiple circuit of relay 500 and applies ground at contacts 536, thereby preparing circuits for motor magnet390 andfinder cut-through relay 300.

In operating contacts 32I, relay 326 completes an obvious circuit for line relay33n at contacts 322 a circuit is prepared for the finder cutthrough relay 300, at contacts 323 a circuit .is prepared for the preenergized relay 550 and at contacts 324 completes a circuit for the finder motor-magnet 396, this circuit extending from ground at contacts 536, contacts 54I, 552, conductor 5I1, contacts 325, 301 and through the winding of magnet 390 to battery.

is In operating contacts 33I, line relay 330 completes an obvious circuit for the slow to release hold relay 340. In operating contacts 34I, hold relay 543 prepares a circuit for operating the line andcut-oii relay I60 completely, at contacts 342 a pulsing circuit is prepared to the connector motor-magnet 490 and at contacts 343 a point in the release circuit of the motor-magnet 490 is opened.

. During the operation in the proceeding paragraph, magnet 390 in operating completes an obvious circuit to the interrupter relay 540 at contacts 39I. Relay 540, in operating contacts 54I, opens the previously traced operating circuit of magnet 390, allowing magnet 396 to restore. In restoring, magnet 390 advances rotary wipers 326, 321, 328 and 329 one step, and opens the circuit to relay540 by way of contacts 39L In restoring, relay 540 again completes the previously traced circuit to magnet 390by way of contacts 54L Magnet 390 reenergizes and at contacts 39I again completes the circuit to relay 540. Relay 540 energizes and at contacts 54I opens the circuit to magnet 390 allowing it to restore, In restoring, magnet 390 advances wipers 325, 321, 328 and 329 a second step and at contacts 39I again opens the circuit to relay 5 .0 allowing it to restore. This interaction between magnet390 and relay 540 continues until wiper 328 engages the contact terminating control conductor I56, at which time a circuit is completed for the preenergized relay 55 0, this circuit extending by way of ground at contacts 555, upper winding of relay 550, conductor 521, contacts 323, wiper 328 and its engaged contact, conductor I55, cable C-I10, conductor I56, .r contact I52 and the lower winding of relayIIiO to battery.

In operating contacts 552, relay 550 opens the circuit to magnet 360 and at contacts 55ll completes a circuit to the finder cut-through relay 333, thiscircuit extending from ground at con-- tacts 538, contacts 541, 55| conductor 531, contacts 332 and the winding of relay 300 to battery. At contacts 553 an obvious circuit is'completed to the total call meter 585 for registering each call and at contacts 554 a locking circuit of relay 510 is opened. It is to be remembered that wipers 323, 321, and 323 are also resting on contacts in their respective banks corresponding to the contact upon which wiper 328 is resting.

In operating contacts 3M and 303, finder cutthrough relay 335 completes the extension of the talking conductors from the calling line with the finder-connector link, at contacts 332 a circuit is completed for the transmission of dial tone out over the positive talkin conductor to the calling station as an indication of readiness by the link to receive dialing. 'At contacts 304, relay 3% completes the circuit for the complete operation of relay I55, this circuit extending from ground at contacts 34!, contacts 354, wiper 328 and its associated contact, conductor I55, cable C516, conductor Hi6, X contacts IE2 and the lower Winding of relay I53 to battery. The closingof contacts 334 also shunts the upper winding of relay 553, but since relay555 has operated, it will remain so bythe holding effect of its lower winding. The ground potential at contacts 3M busies subscriber D to other finders and is also applied to the rotary connector switch by way of conductor I56 to busy subscriber D to incoming calls. At contacts 305, relay 300 completes an obvious holding circuit for itself by way of ground at contacts 34L At contacts 3133, relay 330 prepares a future locking circuit for relays 380 and 400, and supplies a working ground for various other relays in the finder-connector link, at contacts 331 the interrupting circuit to motor-magnet 393 is opened, at contacts 308 a circuit is completed for energizing motor-magnet 515, this circuit extending from ground at contacts 308, conductor 531, contact and engaged with wiper 535, contacts 532 and the winding of magnet 515 to battery, and at contacts 309 a point in the circuit of all-links-busy relay 5% is opened. In energizing, magnet 515 opens a point in the normal operating circuit of the distributor start relay 5H) at contacts 516;

In operating completely (second-step), at contacts l5! and I63, relay I63 opens its previously traced first-step operating circuit, contacts I64 removes ground from the distributor start conductor 13B andrelay 5H! restores. In restoring contacts 5! I, relay 5H3 closes a point in the normal operating circuit of magnet 515, at contacts 5H3 the circuit to relay 523 is opened allowing it to restore, at contacts 5M, a ground is removed from the multiple circuit of relay 500, at contacts 515 ground is removed from the previously opened circuit of relay 558 and at contacts 5I6 the preenergizing and hold circuit of relay 550 is opened, allowing relay 550 to restore. In restoring, relay 553 opens the energizing circuit of relay 300 at contacts 55! and at contacts 553 opens the circuit to meter 585. Relay 300, however, remains energized over its previously traced locking circuit.

In restoring, relay 52!) opens the circuit to relay 533 at contacts 52!. In restoring, relay 533 opens the circuit to relay 320 at contacts 53, at contacts 532 opens the holding circuit for magnet 515, allowing magnet 515 to restore and rotate its-wipers one step. 'At contacts 535 a ground is removed from thernultiple circuit to relay 53B and at contacts 536 the operating circuit of magnet .390 is further opened. Magnet .515 will ro-- tate its wipers until wiper 505 encounters a contact (each corresponding to a finder-connector link) which contains no ground potential and stops thereon.

In restoring, relay 320 opens contacts 32l to remove the bridge from relay 330, but relay 33E! remains operated from the closed loop of subscriber D. At contacts 322 the energizing circuit of relay 300 is further opened by relay 320, but relay 300 remains operated over a previously traced circuit from ground at contacts 34L At contacts 323 relay 320 further opens the operate circuit of relay 550 .and at contacts 324 the energizing circuit of motor-magnet 390 is further opened.

As previously mentioned, dial tone has been transmitted .back to the calling subscriber which is an indication that the desired number may be dialed and in this case the two-digit number 32 that has been assigned subscriber B will be dialed.

The tens digit 3 is dialed and the line relay 333 (energized at the beginning of dialing) will deenergiz and energize upon receipt of each pulse, for a total of three times each. At the beginning of the first pulse and upon deenergizing, relay 33E! opens the circuit to relay 340 at contacts 33I, but relay 340 is slow-to-release and therefore holds operated during dialing. At contacts 332 a circuit is completed to relay 413 and. motor-magnet 490, these circuits extending respectively from ground at contacts 332, contacts 342, conductor 356, contacts 481, 435, to the left over conductor 368, contacts 352, conductor 361 and the winding of relay 410 to battery and from ground at contacts 332, contacts 342, conductor 366, contacts 481, 435, to the right over conductor 333 and through the winding of magnet 493 to battery.

In operating, relay 41!] completes an obvious circuit to relay 460 at contacts 411, at contacts 412 ground is removed from wipers 458 and 469 during the pulsing period and at contacts 413, relay 310 completes a circuit for itself efiective during pulsing independent of the busy'relay contacts 435. Motor-magnet 490 energizes and at contacts 49! opens a point'in its interrupter circuit. The interrupter springs of the dialing mechanism have closed and the circuit is again completed to line relay 330 which. reenergizes thus releasing magnet 490 and ending the first pulse. In operating contacts 462, relay 433 prepares a circuit to the busy relay 430 and at contacts 434 the pulsing circuit is maintained complete.

At the end of the first pulse and in operating, relay 330 closes the circuit to relay 343 at con-' tacts 33l and at contacts 332 opens the pulsing circuit to motor-magnet 490 and relay 410. Relay fill remains operated, however, due to its slow-to-release characteristics.

As previously stated, wipers 465 to 469, inclusive, are resting on the home or 26th position of the rotary switch actuated by motormagnet 4%, therefore, as magnet 49B restores, wipers 465' to 469 inclusive are advanced one step, with the lower halves of the wipers disengaging their respective contacts and the upper halves of the wipers engaging the first contact of each bank. Off-normal springs 415 close as the wipers leave their home positions and com-.

plete a circuit to relay 350.

' In operatingcontacts 35I, relay 353 removes dial tone from the calling line, at contacts 352 the former energizing circuit for relay 410 is opened, at contacts 353 a ground is maintained on the conductor from the seized finder to a contact of wiper 565, at contacts 354 ground is removed from the conductor to the all-links-busy relay 566 and at contacts 355 a point in the self interrupter circuit to magnet 496 is prepared.

At the beginning of the second pulse, the circuit to line relay 336 is again opened, which upon deenergizing completes the formerly traced energizing circuit to motor-magnet 466 and the holding circuit to relay 416 at contacts 332. However, the circuit path to the latter has been altered with the respect that closed contacts 413 have replaced opened contacts 352. This has no apparent effect because as previously stated, relay 416 remains operated during pulsing of each digit dialed. Magnet 466 energizes and opens its self-interrupter circuit at contacts 49!. This interrupter circuit has no effect on the operation at the present and will be discussed later. At the end of the second pulse line relay 336 again energizes and opens the circuit to magnet 466 at contacts 332. In restoring, magnet 436 rotates wipers 465 to 466 inclusive, a second step, at which time the wipers are resting on the second contact of the wipers respective banks.

At the beginning of the third pulse, line relay 336 again deenergizes and completes a conduit, by way of contacts 332, to motor-magnet 496 which then energizes. At the end of the third pulse elay 336 again energize and opens the circuit to magnet 466 at contacts 332. In restoring, magnet 496 rotates wipers 465 to 466 inclusive, a third step, at which time the wipers are resting on the third contact of the wipers respective banks. The dialing of the tens digit 3 has now been completed and the circuit to relay 416 has been opened at contacts 332, thus relay 416 will restore before the second digit has been dialed.

In restoring, relay 416 opens the circuit to relay 466 at contacts 41] thereby allowing relay 466 to restore, at contacts 412 ground is restored to wipers 466 and 469 and a circuit is thereby completed to relay 466, this circuit extending from ground at contacts 366, conductor 365, contacts 412, wiper 466 and engaged contact, conductor 348, contact 384 and through the winding of relay 466 to battery. In restoring contacts 46!, relay 466 prepares a, circuit for the lower winding of relay 466, at contacts 462 the circuit to the busy relay 436 is opened.

In operating contacts 462 and 464, relay 466 has prepared for ringing current to be transmitted over the positive talking conductor, which eventually will serve to cause the ringer of station B to operate. As the ringer for station E is on the opposite side of the line, this ringer will not operate. At contacts 463, relay 466 completes its own obvious locking circuit and at contacts 466 a circuit is completed to motor magnet 466, this circuit extending from ground at contacts 366, conductor 365, contacts 412, wiper 469 and its engaged contact, contacts 466, conductor 318,

contacts 381, conductor 316, contacts 488, 491 and the winding of magnet 466 to battery.

In operating, magnet 496 opens its own energizing circuit at contact 46l and thereby restores. In restoring, magnet 466 rotates wipers 465, to 466 inclusive, one step and closes contacts 461, but the circuit to magnet 466 is now open as wiper 469 is resting on an unused (fourth) contact. However, as wiper 468 engages its next (fourth) contact a circuit is completed to relay 366, this circuit extending from ground at contacts 366, conductor 365, contacts 412, wiper 468 and its 10 engaged contact, conductor 346 and through the winding of relay 386 to battery.

In operating contacts 38i relay 386 prepares a circuit for the cut-through relay 486, at contacts 362 a circuit is prepared for the lower winding of the switch-through relay 486, at contacts 383 a circuit is prepared for Executive cut-in which will be discussed later, at contacts 384 the operate circuit of relay 466 is opened, at contacts 386 a locking circuit is completed for relay 366, at contacts 386 a circuit is prepared for relay 416 and at contacts 381 the line-group interrupter circuit to magnet 466 is opened.

Before continuing with the present description, it is thought that the busy test circuit should be described more in detail. When calling into the first line group, as either the first digits 3 or 4 of the call number are dialed, relay 386 is operatedand at contacts 331 completes a busy test circuit to the busy relay 436 from the 4th contact engaged with wiper 46?, conductor 336, contacts 661, conductor 336 contacts 462 and through the winding of busy relay 436 to battery. Now, when calling into the second line group, as either the first digits 5 or 6 the call number are dialed, relay 386 is not operated (because contacts 5 and 6 correspond to lines of the first group which may be busy at the time) until magnet 466 has automatically stepped all its associated wipers to their 15th contacts, at which time relay 386 is operated and at contact 36! completes the above traced busy test circuit. It will be noted that when the first digit of the call number to either line group is 3 or 5, relay 466 will operate to reverse the ring. When the first digit 3 is dialed and after relay 466 operates, magnet 496 steps its wipers to the 4th contacts to operate relay 386. When the first digit 5 is dialed and after relay 466 operates, magnet 496 steps its wipers to the 6th and subsequently to the 15th contacts before relay 386 operates.

The system is now ready for the second or units digit 2, of the call number 32, to be dialed. As the digit 2 is dialed, line relay 336 (energized at the beginning of dialing) will deenergize and energize upon receipt of each pulse, for a total of two times each. At the beginning of the first pulse and upon denergizing, relay 336 opens the circuit to relay 346 at contacts 33l, but as relay 346 is slowto-release, it will hold operated during dialing. At contacts 332 a circuit is completed to relay 436 and motor-magnet 466, these circuits extend respectively; from ground at contacts 332, contacts 342, conductor 366, contacts 481, 435, to the left over conductor 368, contacts 383, conductor 361 and through the winding of relay 416 to battery;

from ground at contacts 332, contacts 342, conductor 366, contacts 481, 435, to the right over conductor 368 and through the winding of magnet 496 to battery. 1

In operating contacts 41!, relay 416 completes a circuit to relay 466, at contacts 412 ground potential is removed from wipers 468 and 466 relays 386 and 466 are locked operated to grounded conductor 365; and at contacts 413 relay 416 slightly alters its previous operate circuit. In operating, magnet 466 opens a point in its interrupter circuit. At the end of the first pulse and in operating, relay 336 opens the circuits to relay 416 and magnet 496. Relay 416, however, is slow-to-release and does not restore during pulsing. In operating contacts 462, relay 466 prepares a circuit for busy relay 436 and at contacts 464 the pulsing circuit is maintained complete in case busy relay 438' should operate before pulsing is completed.

At the beginning of the second pulse and in releasing, relay 338 completes the circuit to magnet 488. Magnet 498-, in operating, opens its in :terrupter circuit at contacts l9I which again have no effect at the present. At the end of the second and final pulse, relay 338 energizes and opens the circuit to magnet 498 and relay 418 at contacts 332. In restoring, magnet 488 rotates wipers see to :89 inclusive, another step. It will be remembered that at the beginning of the last digit to be dialed, wipers 465 through see were resting on the fourth contact of each respective wiper-bank and that the second digit 2 caused i no effect and at contact an the holding circuit of relay ile is opened. During the time that wiper ts? first engages its sixth contact and before the relay 45c has restored, a busy-test of the called line is made. If the called line should bebusy, a ground would be impressed on the called lines control conductor by contacts such as 384 of its associated seized connector. This ground would be encountered by wiper 46'! at its sixth contact and complete a circuit to the busy relay 438, this circuit extending from wiper 461 conductor 338, contacts 38!, conductor 339, contacts G62 and the winding of relay sec to battery. Relay 438, in operating, would close contact 43I for transmitting busy tone out over the positive talking conductor to the calling subscriber, a more detailed description of connection to a busy line being described hereinafter. I-Iowevenfor the present operation, it will be assumed that the called line is not busy, therefore no ground will be encountered by Wiper 461, and busy relay 438 will notoperate.

In restoring, at contacts IEI relay 468 completes an operative series circuit to the cutthrough relay 488 by way of its lower winding and the line and cut-off relay I48 this circuit extending from ground at contacts 382, conductor 31?, down to contacts 455, contacts 432, through the lower winding of relay 488, contacts 486, 46 I conductor 338, contacts 38L conductor 338, wiper as? and its associated contact terminating conductor I86, cable CI80, conductor I88, contacts [I8 and the lower Winding of relay I48 to battery. In operating, relay I48 opens the circuit to its upper winding at contacts I4I, at contacts I42 ground is removed from the positive talking conductor,

at contacts I43 subscriber B is busied at the finder banks, and at contacts I44, ground is removed from the distributor start conductor to prevent the distributor from starting a finder.

In operating, relay 488 first closes as contacts $85 and completes an operative locking circuit for relay 488 byway of its upper winding, this circuit extending from ground at contacts 382, conductor 81?, as. contacts 485 and through the winding of relay 488 to battery. At contacts 48L relay prepares. a circuit for ring-back tone, at contacts 482 and 483 the talking conductors of the called subscriber are connected with those of the seized connector and a circuit is completed for ringing current, this circuit extending from the grounded ringer of subscriber B, the positive talking conductor, contacts H2, H6, conductor 12 I84, cable CI88, conductor I84, sixth bank contact engaged with wiper 466, contacts 483, 424, 4432 and down through the lower winding of the ring cut-off relay 428 to interrupted generator. At contacts 48- 5, relay 488 applies a ground to prepare a circuit through the upper winding of relay 428 and also provides an additional busying ground on the control conductor of subscriber B. At contacts 488, relay 48!] opens the energizing circuit through its lower winding, at contact 48? the pulsing circuit is opened and at contacts 488 the interrupter circuit tomotor-magnet 288 is opened. 7

After a normal interval of ringing over the previously traced circuit at station B, subscriber B answers the call by removing his receiver. The removal of the receiver at station E closes the switch-hook springs (not shown) at the station and completes a direct current circuit through the lower winding of ring cut-off relay 428 for operating the relay. This circuit extends from ground at contacts 484, 42I, 482, wiper 465 and its engaged sixth contact, conductor I8I, cable CI88, conductor I8I, contacts H8, III, negative talking conductor, switch-hook springs at station B, positive talking conductor contacts H2,

H8, conductor I84, cable CI88, conductor I84, wiper 488 and its engaged sixth contact, contacts 483, 424, 482 and through the lower winding of relay 428 to battery at interrupter gen- 'erator.

In operating, relay 428 looks itself operated by closing its x contacts 428, this circuit extending from ground at contacts 484, conductor 338, contacts 38 I, conductor 339, as contacts 426 and through the upper winding of relay 428 to battery. At contacts 423, and 424, ring-back tone and ringing current are removed from the calling and called line respectively, at contacts 422, and 425 the back bridge relay M8 is connected across the called line and the talking conductors of the calling and called line are connected so that conversation'may proceed. Line relay 338 supplies talking battery for the calling party and back bridge relay M8 supplies talking battery for the called party.

After completion of conversation, both stations B and D replace their receivers. The replacing of the receiver at station D disconnects the equipment in the following manner:

The circuit is opened to line relay 338 which restores and opens the circuit to the hold relay 340 at contacts 334. Relay 348, in restoring, releases contacts 34I and opens the locking circuit to relay 388, and at contacts 343 prepares the self interrupted homing circuit of motorrnagnet 498. The removal of ground at contacts 34I also releases line and cut-off relay I88. In restoring, relay 380 opens the locking circuits of relays 888 and 488 at contacts 385 and at contacts 888 removes one of the ground connections from guard lead 561. Relay 388, in restoring removes ground from conductors 31? and 338 by way of contacts 38I and 382, thereby opening the circuits to relays 428 and 480. In restoring contacts 484, relay 480 opens the circuit to relay I48, which restores and at contacts 488 completes the homing circuit to magnet 498, this circuit extending from ground at off-normal springs 415, conductor 3J5, contacts 355, 343, conductor 816, contacts 488, MI and through the winding of magnet 498 to battery. Magnet 498 energizes and opens its circuit repeatedly until it has stepped wipers 485 to 489 inclusive to the 26th or home position, at which time off-normal -to the one shown in Figures 3 and 4 will be use and associated with station B.

gaged with their respective sixth contacts.

- tact, conductor 338,

springs 415 open'and the circuits to magnet 4'96 'andrelay. 350 are maintained open. Relay 423 has restored and the equipment is again at rest and ready forfuture calls.

Executive cut-in :feature will function as describedin the following paragraphs.

It will be assumed-that the subscriber at station B has received or initiated acall and is in a busy condition. A finder-connector identical in Assuming further that this particular executive desires to call station B, his call will be initiated and handled in the same manner as described in the section entitled Regular P. A. X

service, but stopping at the point in the operation where the last digit 2 of the callnumber 32 has been dialed and before the release of the slave relay such as 406. It will also be assumed that the illustrated finder-connector link in Figures 3 and 4, will be used in handling the call placed by said executive.

Continuing now with the explanation: After the last pulse of the dialed digit 2 has been received and motor-magnet 436 has advanced wipers 465 to 469 inclusive, thewipers are en- The circuit to relay 410 has been opened at contacts 332 by the line relay 330 and relay 410 restores.

In restoring, relay 419 opens the circuit to slave relay 460, but relay 460 is slow to release and does not restore immediately, thereby utilizing this time interval to test for busy. As previously stated, station B is busy and therefore wipers 461 will encounter ground at its sixth contact which then completes a circuit for the busy relay 430, this circuit extending from the grounded control conductor, Wiper 461 and engaged concontacts 38I, conductor 339, contacts 462 and the winding of relay 436 to battery.

In operating contacts 43!, relay 430 completes a previously traced busy tone circuit to station A, at contacts 432 an energizing circuit is opened to the lower winding of relay 436 and at contacts I 433, relay 436 prepares alocking circuit for itself.

In restoring as the armature of contact 462 starts to release, a locking circuit is completed for relay 433 by relay 433, this circuit extending from ground at contacts 382, conductor 311, contacts 455, 433, 456, 463 and through the winding of relay 430 to battery.

After hearing busy tone, the executive momentarily depresses his non-locking key I18, thus completing a circuit to the cut-in relay 453, this circuit extending from ground at key I18, conductor I89, cable CI 10, conductor I39, the fifth contact of the rotary finder switch and wiper 329, contacts ,383, 36I, conductor 331, contacts 443 and the winding of relay 450 to battery.

In operating, relay 453 completes the extension of station A with station B at contacts 45I and 453, at contacts 452, busy tone is removed from the calling 1ine, at contacts 454 and 435 the holding circuit of relay 436 is changed back to the original busy ground on the contact of the called line and at contacts 456 a circuit is completed for relay 440 in series with relay 436. The circuit for these two relays may be traced as i4 followsi From ground onwi'per'461, conductor 338, contacts 38!, conductor 339, contacts 454, 433, the winding of relay 440, contacts 463 and the winding of relay 430 to battery. In operating, relay 446 supplies a holding ground for the relay 456 by Way of contacts 442.

The executive has been connected with station B and condensers C4 and C5 may serve as monitoring or talking condensers. The executive may continue to converse with station B or he may request that both parties hang up their receivers, at which time, the busy relay 436 and relay. 443 will restore and the cut-through relay 486 will operate and station B is rung and connected directly with the executive, when B answers the ring, in the usual manner. With a small exchange and a limited number of finder-connector links available, the first method is not desirable, because two links would be in use for the duration of the conversation. For that reason, the second method is preferred, because only one link is used and the other is released to handle other calls. Therefore when station B and his called party release their finder-connector link, station B no longer is busy and ground is removed from wiper 461 and relays 430, 446 and450 restore and at the same time complete a circuit through the lower winding of relay 483 over a path previously traced in the section entitled Regular P. A. X service. The remaining operation of the equipment and the release of the equipment is the same as described in the above-mentioned section.

It will be noted that this special type of service entitles the executive to cut-in over all regular calls.

At'the top of Figure 4 are shown two conduc" tors 331 and M5 labeled thusly-To voice paging. The voice paging equipment is not shown, however, due to certain requirements of the exchange, voice paging may be desired for some stations. A key (such "as I18 shown at station A) may be used to start the voice pagingequipment in the following manner: when the key such as I18 is depressed, operations of the equipment shown in Figures 1, 3 and 4 will take place as described in the above section up to and including the operation of relay 440, at which time the closing of contacts 44I completes a circuit to the start relay (not shown) of the voice paging equipment. This circuit may be traced as follows: from ground at key I18, conductor I89, cable CI16, conductor I89, the 5th contact engaged with wiper 329, contacts 333, 36L coirductor 331, contacts I, conductor M5 and through the winding of the voice paging start relay (not shown) to battery. The start relay then locks operated to conductor 331, by-passing contacts 4.

Upon completion of the voice paging, the operated equipment in Figures 1, 3 and 4 restore a described in the above section.

Code call r The ensuing description of the equipment will cover the addition of the special service feature Code call to the system. This feature is illustrated in Figures 6, '7 and 8 and will be used in combination with Figures 1, 3,4 and 5, including occasional references to the previous section entitled Regular P. A. Xservice.

It will be remembered that certain subscribers whom it is desired to page by code ringing of the code call equipment, areassigned individual designated two-digit code call numbers andthat any subscriber wishing: to initiate a. code. call must prefix the single digit "1" to the code call number of. the desired. subscriber. Only certain stations having their extra control (E.. C.) conductor marked, by havingv it connected to the. code call finder, can. initiate a. code call, whereas a .code call may be answered from any station of thev system. Theprefix digit 1 should be dialed, then; a slight pause to wait for a. second dial tone before. dialing: the code call. number. it. is to be; remembered that the. code call may be answered, by dialing the single digit 2.

It will be. assumed that the subscriber at station A. is an: executive and has. been assigned the code call. number 33-. Assuming'also that the subscriber at station C wishes to talk. with the executive and has dialed the executives regular call number 41, but has been informed. by hissecretary that he-is somewhere at large about the building, The subscriber at station C can now' initiate a code call. for the executive by momentarily replacinghis receiver, then removing. it and dialing the digit 1 and waiting. for dial. tone, prior to dialing the code call number 33.

The operation of the equipment up to and including the, dialing ofthe digit. 1 is the same asthat. in. the section entitled Regular P. A. X service. A short review upon completion of dialing the digit 1 will reveal that wipers. 465

through. 469 have been advanced to engage their respective first contacts; relay 416 has restored contacts 412 and completed circuits to. relays 366- and 366 andv also opened. the circuit to relay 466, the. circuit for relay 366 extends from ground .338, Wiper 461 and engaged first. contact, conductor 18!, cable C696,. conductor 18!, contacts 13!, 152, conductor 608, contacts 65! and the windings of relays 636 and 646 to battery. In

operating contacts 36!, executive cut-in privileges are removed by relay 366, and at contacts 362 prepares an operating circuit for relay 316' and the code call finder. In operating, relay 466 rompletes its own locking circuit by way of. its

upper winding and m contacts 485 over an obvious path, at contacts 464 a maintaining ground is. applied. for the relays 636 and 646,

and at contacts 481 opens the pulsing circuitto motor magnet 496.

In operating, relay 646 operates at the same time or ahead. of relay 636, thereby preventing relay 656 from operating at the present time by opening contacts 64!. At contacts 63!, relay 636 completes a circuit for relay 6!6, this circuit extending from ground at contacts 63!, contacts 62!, 666 and the winding of relay 6!6' to battery.

Contacts 63'! also close a preenergizing circuit for the upper winding of relay 626 through resistor R3 which renders relay 626 extremely fast to operate. is applied for marki'ngthe extra control conductor to prepare for stopping the code call finder 0n the calling line, and. at contacts 633 a circuit is prepared for the relay 656.

In operating, relay 6 !6 completes an obvious Also, ,1

At contacts 632 a battery potential 4 circuit for the motor magnet 665 at contacts 61!. Magnet 665', in operating, opensthe'circuit to relay 6!!) by Way of contacts 666'. In'restoring, relay 6E6 opens the circuit 'to magnet 665 at contacts -6!!. Inrestoring, magnet 665 completes the circuit to relay 616 by way of contacts 666 and rotates wipers 653 through 6I6- one step. Relay 616 again completes the circuit to magnet 665 at contacts 6!! and magnet 665-then opens the circuit to relay 626 at contacts 666. In restoring contacts 6H relay 6!!) opens the circuit to magnet 665 and in restoring, magnet 665 again completes the circuit to relay 6I-6 at contacts 666 and again rotates-wipers 6 I3 through 6l6 one more step. This inter-action continues until the last releaseof magnet 665 rotates wiper 6!6 to engage the contact terminating conductor 364, at which time a circuit is completed for the preenergized relay 626 in series with relay316,

this circuit extending from ground atrelay 316 and through its winding; conductor 346, contacts 434, conductor 345, contacts 362, 383, wiper 329 and engaged contact, conductor 364, cable C3! conductor 364, the contact engaged by wiper 616, lower winding of relay 626 and contacts 632 to battery. Relay 626 operates before relay 6i6-has had time to reoperate and opensrthe circuit to relay 6!6 at contacts 62!, at contacts 622 the resistance R--3 is shunted to complete an obvione looking circuit for relay 626 by way of its upper winding and at contacts 623 a ground is applied to the control conductors of station C to maintain the line and cut-oil" relay I56 operated and to busy station C to all incoming calls.

In operating contacts 311 relay 316 initiates the release of the illustrated finder-connector link (which has been seized by station C") by releasing relay 366, which nowdisconnectsthe talking conductors of station C from the line relay 336 of the regular finder-link at contacts 36! and 363 and at contacts 366 ground is removed from conductor-365 allowing relay 386 to restore. Line relay 336 restores and opens the circuit to slow to release relay 346. Relay 386 opens the locking circuit of relay 466 at contacts 382 and at contacts 383 opens the circuit to the lower winding of relay 626 which now remains operated over its upper winding, the same contacts (383) open the circuit to relay 316. In restoring contacts 484, relay 486 removes the holding ground from relays 636 and 646 and at contacts 488 the self-interrupting circuit for motor magnet 496 is prepared. Relay 346' now has restored and at contacts 343 completes the self-interrupting circuit for motor magnet 496. l\ Iagnet 496 restores wipers 465 through 469 to their home position in the manner as described in the section entitled Regular-P. A. X service,

and off-normal springs 415 are opened, thereby breaking the circuit to relay 356. The finderconnector link isnow completely restored and conditioned to handle future calls.

Referring'now to the code call equipment, re-

lay 646 restores ahead of the slow-to-release relay 636, thereby completing an obvious circuit to relay 656 by way of contacts 64!. Iii-operating, at contacts 65!, relay 656 further opens the circuit to relays 636 and 646', at contacts. 652 ground is applied to the control conductor 18! for busying the :code call equipment, at contacts 653a point in an alarm circuit is opened, at con.- tacts 654 and 655 the talking conductors of the calling station C are bridged across and operate line relay 660 and at contacts 656 dial tone is projected out over the negative talking conductor 

